The recent boom in renewable energy has given rise to power plants whose fuel source is the Sun. Some plants, for example, concentrated solar power (CSP) plants, use multiple solar receivers with associated heliostat fields distributed over large geographical areas to produce steam. A commercial CSP plant might consist of ten or more receivers, each powered by a field of 20,000 to 30,000 heliostats. Steam produced by the receivers is piped to a power block that may include a steam turbine generator (STG), or to another steam consumer, e.g., a combined cycle plant.
Due to varying amounts of flux throughout the course of a day, a CSP plant will start up and shut down daily. The startup time for a CSP plant may, for example, be as high as two hours per day, which means that 20% of all available operating hours may be devoted to startup. Startup time may be further delayed by variables such as ambient temperature, wind, and clouds.
Once a CSP plant is running and generating power, it is still vulnerable to load swings during the running operation due to using the Sun as a power source. Changes in the weather, especially clouds, can have large effects on plant operation. For example, a cloud transient may reduce or increase power delivery by 80% or more in only a few minutes. A CSP plant may even become unstable as a result of a rapid oscillation of power delivery which may generate high thermal stresses on CSP plant equipment.
Cloud transients may cause additional problems when a CSP is spread over a large geographic region, for example, 250 acres or more, because the incident flux on the receivers may not be uniform. This may result in a large variance in operating capacity of any receiver at any given time. Furthermore, CSP plants may have less stored energy in the system to handle load changes among receivers. It may also be very difficult to store energy overnight in the receivers without large losses.